Regular physical activity (PA), adequate gestational weight gain (GWG), and healthy eating are important for the long-term health of both mother and baby. Hence, it is important that women receive current and updated advice on these topics and are encouraged to adopt a healthy lifestyle during pregnancy.The aim of this study was to investigate the main information sources among pregnant women regarding PA, GWG, and nutrition as well as to evaluate how these information sources may affect their health behaviors.A cross-sectional study design, comprising an electronic questionnaire, was distributed to 2 antenatal clinics, as well as pregnancy-related online chat forums and social media. The inclusion criteria were ≥18 years, ≥20 weeks gestation, and able to read and write Norwegian. In total, 150 pregnant women answered the questionnaire, which was a mix of 11-point Likert scales, close-ended questions, and semi-close-ended questions with the option to elaborate. The relationship between information sources and selected variables, including health behaviors and descriptive variables, were assessed by logistic regression, linear regression, or chi-square as appropriate (P<.05).Mean age (years), gestation week, and prepregnancy body mass index (kg/m) were 31.1 (SD 4.3), 30.6 (SD 5.9), and 24.2 (SD 4.2), respectively. More than eight out of 10 had received or retrieved information about nutrition (88.7%, 133/150) and PA (80.7%, 121/150), whereas 54.0% (81/150) reported information on GWG. When combining all 3 lifestyle factors, 38.5% had retrieved information from blogs and online forums and 26.6%, from their midwife or family physician. Women who reported the internet and media as their primary source of information on weight gain had increased odds of gaining weight below the Institute of Medicine (IOM) guidelines compared with gaining within the guidelines (odds ratio [OR] 15.5, 95% CI 1.4-167.4; P=.02). Higher compliance with nutritional guidelines was seen among those who cited the internet and media as their main source of information on nutrition (beta=.7, 95% CI 0.07-1.3; P=.03). On the other side, receiving advice from friends and family on weight gain was significantly associated with gaining weight above the IOM guidelines compared with gaining within the guidelines (OR 12.0, 95% CI 1.3-111.7; P=.03). No other associations were found between information sources and health behaviors.The small number of health professionals giving information and the extensive use of internet- and media-based sources emphasize the need to address the quality of internet advice and guide women toward trustworthy sources of information during pregnancy. The association between information sources and PA, GWG, and nutrition requires further research.